DNA Error Checking Evolves
Matt and
George's debate about mutation brought an idea to mind. Here it is for you guys to shoot down if I'm "out to lunch."
During times that the environment is stable - the climate is stable and and a particular species' niche is well-defended and other niches are unavailable, there is selective pressure to improve error checking within that species so as to decrease mutations. This slows evolution to a crawl.
When the environment is unstable there is selective pressure to decrease DNA error checking. This will speed evolution.
This is how the selective pressure is brought to bear:
Let's say two individuals, A and B, are born into a species that is well-adapted to a niche within a stable climate and other niches are unavailable. A is born with DNA error checking efficiency of 95% and B has DNA error checking efficiency of 97%. Other than this difference let's assume that A and B are identical. Let's also assume that both A and B are successful at having children and that their children inherit the DNA error checking efficiency of their respective fore-bearers.
As time passes B's descendents will be marginally more successful than A's descendents. Why? Because B's family will have fewer mutants. And a mutation is not likely to be beneficial when the climate is stable and the niche is well-defended and other niches are unavailable. Under these circumstances greater error checking efficiency is a positive adaptation. B's family prospers as A's family begins to lose ground to B.
But then something happens. The climate changes, the dinosaurs are wiped out, whatever. Both the population of family A and family B plummet. But after a long time it is A's family that rebounds while family B flirts with extinction. Why? Family A is in a better position to quickly adapt to the changing environment. Family A has more mutants than B and any given mutation has a greater chance of being beneficial in this new environment. The old adaptations no longer serve in the new environment. Both A and B must change, but A is better able to do so.
In times of crisis niches will open up. Family A will also be in a better position to exploit the new ground.
This idea is almost certainly old news. Could someone point me to more information on it?
Posted by Stephen Gordon at April 8, 2004 12:39 AM
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A good area to check out is the breeding of animals (same goes for plants but I'll consider just animals). It turns out that the various characteristics (looks, health, personality, weight, etc) that people breed animals for usually require significant winnowing to achieve. Once some degree of the desired characteristics is achieved, then the breeder can pull in outside animals with complementary characteristics and breed those in. The key apparently is to breed in outside animals at a slow rate so that "pureness" of the breed remains stable.
Finally, the best animals often are hybrids which in this case means crosses between pure breeds. There are systems for breeding in three or more pure breeds into a hybrid population. What's interesting is that the pure breeds remain more valuable than the hybrids. One can regenerate the hybrid stock from the pure breeds, but the pure breeds can't be regenerated from the hybrids.